Asbestos is an industrial mineral of fibrous nature and is a term collectively used to include such minerals as chrysotile, crocidolite, amosite, and anthophyllite. All of these minerals are hydrated silicates which generally contain substitutional iron, calcium, magnesium, and sodium in various proportions. Chrysotile represents approximately 95% of all asbestos mineral consumed for industrial and commercial purposes and may be represented by the formula: Mg.sub.3 Si.sub.2 O.sub.5 (OH).sub.4. Similarly, crocidolite, amosite and anthophyllite may be represented by the formulas Na.sub.6 Fe.sub.10 Si.sub.16 O.sub.46 (OH).sub.2, (FeMg).sub.7 Si.sub.8 O.sub.22 (OH).sub.2 and Mg.sub.7 Si.sub.8 O.sub.22 (OH).sub.2, respectively. Variation in mineral chemistry and physical characteristics of asbestos has been reported and may be attributable to changes in substitutional calcium, iron, magnesium and sodium represented in the general asbestos mineral formula: (Na, Ca, Fe, Mg)Si.sub.x O.sub.y (OH).sub.z.
As a toxic mineral, various attempts have been made to render asbestos inert. Attempts to destroy asbestos waste using heat alone to alter asbestos fiber chemistry have been met with only limited success since asbestos fibers by their very nature are refractory. For example, chrysotile fibers have been reported to withstand temperatures up to 3000.degree. F. for time periods of up to one-half hour. Since such a technique requires very high temperatures for fiber destruction, this approach has proved quite uneconomical.
A method utilizing reduced process temperatures is described in U.S. Pat. No. 4,678,493. In that patent, asbestos waste is converted to glass (i.e., vitrified) by mixing the asbestos waste with a melt accelerator and waste glass cullet, then melting the mixture to form a glassy substance.
Vitrification processes require that the raw material remain reasonably constant in both chemical and physical properties. For this reason, conversion of asbestos to glass requires tight control over raw material input, including control over the particle size of the raw material. This degree of control is difficult to maintain economically in asbestos waste processing. A primary reason for this difficulty is that asbestos fibers have traditionally not been used alone in the preparation of refractory insulations, electrical insulations, building materials and other products. Rather, they have been combined with materials such as fiberglass, calcium silicates, water-soluble silicates, portland cements, clays, calcium sulfate (gypsum), silica, lime, oxychloride-bonded dolomites and a variety of other components. Thus, asbestos content by weight may vary from 5% or less to almost 100% of these composite materials.
Owing to the diverse mixture possibilities encountered in actual commercial applications, it is difficult to control the vitrification process unless the amount of asbestos waste entering the process is kept low relative to the amount of glass formers required. For example, asbestos waste must be kept as a minor component to mitigate the impact of variation in raw material chemistry. Alternatively, the type of asbestos waste entering the vitrification process needs to be controlled to preclude wide variation in raw material chemistry. Thus, the vitrification of asbestos is difficult to render economically feasible.
Disposal methods for asbestos waste in the United States typically involve landfill in a monofill dump site specifically designed to contain only asbestos waste or in hazardous waste landfill sites. Owing to landfill bans, disadvantages associated with committing material to landfill dumping, and a resolve by regulatory authorities to minimize utilization of landfills of all types, there is a need in the art for a process which will convert asbestos waste into a non-asbestos product without the disadvantages associated with the prior art techniques.